1. Field of the Invention
The present invention is directed to electrical fuse link assemblies that are separated under tension, and in particular to such assemblies that have a strain relief member disposed in parallel with the fuse link.
2. Brief Description of the Prior Art
Such fuse link assemblies are usually operated at high voltages, typically 1 Kv and above. The tensioning of the fuse link provides current-clearing mechanical separation of the melted fuse link portions. It was discovered however, that if the fusible element is made to carry the tensile load, its designed fusing action would be altered. Strain relief members are, therefore, added in parallel to the fusible member to remedy this problem.
Because the strain relief members are made of conductive materials, it is convenient to form them from material having a much higher electrical resistance than the fusible member so as not to alter fuse operation. More importantly, this arrangement provides a dual action fuse operation, wherein a time delay fusing is provided for low energy, light overloads, while an instantaneous fusing is provided for higher energy, heavy overloads.
The present invention is directed to the securing of fusible and strain relief members in an operable fuse link assembly. Heretofore, this securement required a solder or other eutectic alloy connection to form a meltable weak spot. One example of such an arrangement is found in U.S. Pat. No. 2,859,307 issued to J. W. Enk on Nov. 4, 1958, which is directed to an improved, stronger soldered junction. In one embodiment, fusible conductor members are joined at their overlaping free ends in a junction block having a particular configuration. The junction block consists of two very large diameter cylindrical crimp tubes each of which receive a free end of a fusible conductor, and are thereafter deformed into a trough-like shaped having a cresent-like cross section. The two crimp tubes are arranged to overlie each other, with one crimp tube nested within the other, and are joined together by an intervening layer of solder. On a light overload, insufficient to fuse either conductor member, heat is transmitted to the intervening solder layer which would eventually melt, thereby providing a fusing action to break the overload current. As contemplated by the invention, the diameter of the crimp tube was many times larger than the diameter of the conductor received therein. This arrangement, according to the teaching of the patent, diffuses the heat generated in the fusible conductor ends so as to prevent localized erratic high temperature buildup in the solder. The crescent shaped crimp portions also provide an enhanced solder joinder between the crimp members, due to the complementary shape and nesting arrangement provided. In addition, the crescent shapes provide a more compact junction block which could fit within a smaller diameter outer insulating tube which surrounds the completed fuse link assembly.